It is well-known that bisphenol A is an important compound as a starting raw material for epoxy resin or an engineering plastic such as polycarbonate resin and polyarylene resin, and accordingly it tends to increasingly expand its demand year by year.
Bisphenol A is produced by the condensation reaction of excess phenol with acetone in the presence of an acidic catalyst and as the case may be, a sulfur compound as a cocatalyst.
There has heretofore been employed an inorganic mineral acid such as sulfuric acid and hydrogen chloride as an acid catalyst to be used in the reaction. In recent years, however, attention has been paid to cationic exchange resins (refer to UK Patent GB 842209, 849565 and 883391), which have been brought into industrial applications.
On the other hand, it is known that useful sulfur compounds to be used as a cocatalyst include alkyl mercaptans with or without a substituent group such as methyl mercaptan, ethyl mercaptan and thioglycol acid ( refer to U.S. Pat. Nos. 2,359,242 and 2,775,620). The mercaptans have a function of increasing the rate of reaction and at the same time, enhancing the selectivity. For instance, in the production of bisphenol A, there are formed as a reaction by-product, 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)-propane (o, p′-isomers) as a principal component and in addition thereto, trisphenol and polyphenol. In particular, bisphenol A, when being employed as a starting raw material for polycarbonate resin or polyarylene, is required to be minimized in contents of the above-mentioned by-products, highly pure and free from coloration. As such, the mercaptans are employed to increase the rate of reaction, suppress the formation of the by-products, and enhance the selectivity.
However, the mercaptans cause corrosion of equipment and involve environmental and sanitary problems such as odor. In recent years therefore, use is made as a catalyst, of a variety of acid type modified ion exchange resins in which a sulfur-containing group is introduced in part of its sulfonic acid group in place of the combinational use of the aforesaid cation exchange resin and mercaptans.
There is known as one of the aforesaid acid type modified ion exchange resin, an acid type ion exchange resin which is modified in part with a sulfur-containing amine compound. In the case however, where bisphenol A is produced by the condensation reaction of phenol and acetone in the presence of a catalyst composed of the foregoing acid type ion exchange resin which is modified in part with a sulfur-containing amine compound, there is brought about a problem in that the activity of the catalyst is deteriorated by methanol as an impurity in acetone. In order to solve the aforesaid problem, there is proposed a method for suppressing the deterioration of the catalyst by allowing a small amount of water to be present in the starting raw material for reaction (refer to Japanese Patent Application Laid-Open Nos. 172241/1994 (Heisei 6), 175898/1998 (Heisei 10), 251179/1998 (Heisei 10) and 251180/1998 (Heisei 10). Nevertheless, the foregoing method can not be said to be always satisfactory, since the deterioration of the catalyst is newly brought about by water, thus making it impossible to sufficiently exert the effect on suppressing the deterioration of the catalyst.
On the other hand, there is proposed a method for decreasing the content of the compound as impurities in the starting raw material to less than 0.1% by weight by subjecting the starting raw material for reaction to refining treatment, said compound being represented by the formula: R—X, wherein R is an alkyl group, an alkenyl group, a cycloalkyl group or a cycloalkenyl group, and X is OH, a halogen atom, a carboxylate group, a sulfate group or a sulfonate group. Nevertheless, the method just mentioned can not be said to be always satisfactory, since it is obliged to subject phenol and acetone as the starting raw materials to refining treatment, thereby increasing the refining steps thereof.